{"id":"CVE-2021-20235","aliases":["BELL-CVE-2021-20235","DEBIAN-CVE-2021-20235","DLA-2588-1","EUVD-2021-7674","GHSA-fc3w-qxf5-7hp6","GHSA-hrfc-mjc4-cv8f","JLSEC-2026-515","UBUNTU-CVE-2021-20235","USN-4920-1"],"status":"published","title":"There's a flaw in the zeromq server in versions before 4.3.3 in src/decoder_allocators.hpp. The...","description":"There's a flaw in the zeromq server in versions before 4.3.3 in src/decoder_allocators.hpp. The decoder static allocator could have its sized changed, but the buffer would remain the same as it is a static buffer. A remote, unauthenticated attacker who sends a crafted request to the zeromq server could trigger a buffer overflow WRITE of arbitrary data if CURVE/ZAP authentication is not enabled. The greatest impact of this flaw is to application availability, data integrity, and confidentiality.","severity":{"version":"3.1","score":8.1,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"high","assessor":"primary","from":"nvd"},"epss":{"day":"2026-11-11","score":0.43862,"percentile":0.98764,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-120","CWE-787"],"published":"2021-03-09T00:00:00Z","modified":"2026-10-24T10:50:40Z","fixes":[{"ecosystem":"Debian:12","package":"zeromq3","fixed_in":["4.3.3-1"],"sources":["osv"]},{"ecosystem":"Debian:13","package":"zeromq3","fixed_in":["4.3.3-1"],"sources":["osv"]},{"ecosystem":"Debian:14","package":"zeromq3","fixed_in":["4.3.3-1"],"sources":["osv"]},{"ecosystem":"Julia","package":"ZeroMQ_jll","fixed_in":["4.3.4+0"],"sources":["osv"]},{"ecosystem":"Ubuntu:Pro:18.04:LTS","package":"zeromq3","fixed_in":["4.2.5-1ubuntu0.2+esm2"],"sources":["osv"]},{"ecosystem":"Ubuntu:Pro:20.04:LTS","package":"zeromq3","fixed_in":["4.3.2-2ubuntu1.20.04.1~esm2"],"sources":["osv"]}],"affected":[{"source":"osv","ecosystem":"Debian:12","package":"zeromq3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.3.3-1"}]}]},{"source":"osv","ecosystem":"Debian:13","package":"zeromq3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.3.3-1"}]}]},{"source":"osv","ecosystem":"Debian:14","package":"zeromq3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.3.3-1"}]}]},{"source":"osv","ecosystem":"Debian:9","package":"zeromq3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.2.1-4+deb9u4"}]}],"versions":["4.2.1-4","4.2.1-4+deb9u1","4.2.1-4+deb9u2","4.2.1-4+deb9u3"],"bundled":2},{"source":"osv","ecosystem":"Julia","package":"ZeroMQ_jll","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"4.3.4+0"}]}]},{"source":"osv","ecosystem":"Ubuntu:Pro:18.04:LTS","package":"zeromq3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.2.5-1ubuntu0.2+esm2"}]}],"versions":["4.2.1-4ubuntu1","4.2.2-1ubuntu2","4.2.3-1","4.2.3-1build1","4.2.5-1","4.2.5-1ubuntu0.1","4.2.5-1ubuntu0.2","4.2.5-1ubuntu0.2+esm1"]},{"source":"osv","ecosystem":"Ubuntu:Pro:20.04:LTS","package":"zeromq3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.3.2-2ubuntu1.20.04.1~esm2"}]}],"versions":["4.3.2-1","4.3.2-2","4.3.2-2ubuntu1","4.3.2-2ubuntu1.20.04.1~esm1"]},{"source":"osv","ecosystem":"Ubuntu:Pro:14.04:LTS","package":"zeromq3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.0.4+dfsg-2ubuntu0.1+esm3"}]}],"versions":["3.2.3+dfsg-2","3.2.4+dfsg-1","3.2.4+dfsg-2","3.2.4+dfsg-3","3.2.4+dfsg-4","4.0.3+dfsg-1","4.0.4+dfsg-2","4.0.4+dfsg-2ubuntu0.1","4.0.4+dfsg-2ubuntu0.1+esm1","4.0.4+dfsg-2ubuntu0.1+esm2"],"bundled":5},{"source":"osv","ecosystem":"Ubuntu:Pro:16.04:LTS","package":"zeromq3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.1.4-7ubuntu0.1+esm2"}]}],"versions":["4.0.5+dfsg-3ubuntu1~gcc5.1","4.0.5+dfsg-3ubuntu2","4.1.4-7","4.1.4-7ubuntu0.1","4.1.4-7ubuntu0.1+esm1"],"bundled":5},{"source":"osv","ecosystem":"Ubuntu:Pro:18.04:LTS","package":"zeromq3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.2.5-1ubuntu0.2+esm2"}]}],"versions":["4.2.1-4ubuntu1","4.2.2-1ubuntu2","4.2.3-1","4.2.3-1build1","4.2.5-1","4.2.5-1ubuntu0.1","4.2.5-1ubuntu0.2","4.2.5-1ubuntu0.2+esm1"],"bundled":5},{"source":"osv","ecosystem":"Ubuntu:Pro:20.04:LTS","package":"zeromq3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.3.2-2ubuntu1.20.04.1~esm2"}]}],"versions":["4.3.2-1","4.3.2-2","4.3.2-2ubuntu1","4.3.2-2ubuntu1.20.04.1~esm1"],"bundled":5}],"products":[{"vendor":"microsoft","product":"zeromq"},{"vendor":"zeromq","product":"libzmq"}],"references":[{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=1921983","tags":["x_refsource_MISC","x_transferred","Issue Tracking","Patch","Third Party Advisory","fix","web"]},{"url":"https://github.com/zeromq/libzmq/security/advisories/GHSA-fc3w-qxf5-7hp6","tags":["x_refsource_MISC","x_transferred","Patch","Third Party Advisory","fix","web","report"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-20235"},{"url":"https://github.com/advisories/GHSA-hrfc-mjc4-cv8f"},{"url":"https://docs.bell-sw.com/security/cves/CVE-2021-20235","tags":["advisory"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2021-20235","tags":["advisory"]},{"url":"https://ubuntu.com/security/CVE-2021-20235","tags":["report"]},{"url":"https://ubuntu.com/security/notices/USN-4920-1","tags":["advisory"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2021-20235","tags":["report"]},{"url":"https://ubuntu.com/security/CVE-2019-13132","tags":["report"]},{"url":"https://ubuntu.com/security/CVE-2020-15166","tags":["report"]},{"url":"https://ubuntu.com/security/CVE-2021-20234","tags":["report"]},{"url":"https://ubuntu.com/security/CVE-2021-20237","tags":["report"]}],"sources":{"cve":[{"id":"CVE-2021-20235","description":"There's a flaw in the zeromq server in versions before 4.3.3 in src/decoder_allocators.hpp. The decoder static allocator could have its sized changed, but the buffer would remain the same as it is a static buffer. A remote, unauthenticated attacker who sends a crafted request to the zeromq server could trigger a buffer overflow WRITE of arbitrary data if CURVE/ZAP authentication is not enabled. The greatest impact of this flaw is to application availability, data integrity, and confidentiality.","status":"published","published":"2021-04-01T13:47:05Z","modified":"2024-08-03T17:37:22.831Z","cwes":["CWE-120"],"updated_at":"2026-11-02T14:32:55.564736Z"}],"euvd":[{"id":"EUVD-2021-7674","description":"There's a flaw in the zeromq server in versions before 4.3.3 in src/decoder_allocators.hpp. The decoder static allocator could have its sized changed, but the buffer would remain the same as it is a static buffer. A remote, unauthenticated attacker who sends a crafted request to the zeromq server could trigger a buffer overflow WRITE of arbitrary data if CURVE/ZAP authentication is not enabled. The greatest impact of this flaw is to application availability, data integrity, and confidentiality.","status":"published","published":"2021-04-01T13:47:05Z","modified":"2024-08-03T17:37:22Z","updated_at":"2026-11-03T03:25:09.355483Z"}],"ghsa":[{"id":"GHSA-hrfc-mjc4-cv8f","title":"There's a flaw in the zeromq server in versions before 4.3.3 in src/decoder_allocators.hpp. The...","description":"There's a flaw in the zeromq server in versions before 4.3.3 in src/decoder_allocators.hpp. The decoder static allocator could have its sized changed, but the buffer would remain the same as it is a static buffer. A remote, unauthenticated attacker who sends a crafted request to the zeromq server could trigger a buffer overflow WRITE of arbitrary data if CURVE/ZAP authentication is not enabled. The greatest impact of this flaw is to application availability, data integrity, and confidentiality.","status":"published","published":"2022-05-24T17:46:03Z","modified":"2023-01-27T05:03:37Z","cvss":[{"version":"3.1","score":8.1,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"high"}],"cwes":["CWE-120","CWE-787"],"updated_at":"2026-11-02T14:42:17.140708Z"}],"nvd":[{"id":"CVE-2021-20235","description":"There's a flaw in the zeromq server in versions before 4.3.3 in src/decoder_allocators.hpp. The decoder static allocator could have its sized changed, but the buffer would remain the same as it is a static buffer. A remote, unauthenticated attacker who sends a crafted request to the zeromq server could trigger a buffer overflow WRITE of arbitrary data if CURVE/ZAP authentication is not enabled. The greatest impact of this flaw is to application availability, data integrity, and confidentiality.","status":"published","published":"2021-04-01T14:15:13.217Z","modified":"2026-06-17T03:33:31.373Z","cvss":[{"version":"3.1","score":8.1,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"high","assessor":"primary"},{"version":"2.0","score":6.8,"vector":"AV:N/AC:M/Au:N/C:P/I:P/A:P","level":"medium","assessor":"primary"}],"cwes":["CWE-120","CWE-787"],"updated_at":"2026-11-02T14:06:51.197859Z"}],"osv":[{"id":"BELL-CVE-2021-20235","title":"CVE-2021-20235 does not affect BellSoft software","status":"withdrawn","published":"2021-04-01T14:15:00Z","modified":"2026-01-26T09:48:10.512503Z","cvss":[{"version":"3.1","score":8.1,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"high"}],"updated_at":"2026-11-02T15:28:15.925958Z"},{"id":"CVE-2021-20235","description":"There's a flaw in the zeromq server in versions before 4.3.3 in src/decoder_allocators.hpp. The decoder static allocator could have its sized changed, but the buffer would remain the same as it is a static buffer. A remote, unauthenticated attacker who sends a crafted request to the zeromq server could trigger a buffer overflow WRITE of arbitrary data if CURVE/ZAP authentication is not enabled. The greatest impact of this flaw is to application availability, data integrity, and confidentiality.","status":"published","published":"2021-04-01T14:15:13.217Z","modified":"2026-10-24T10:50:40.240694847Z","cvss":[{"version":"3.1","score":8.1,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"high"}],"updated_at":"2026-11-02T15:44:18.004149Z"},{"id":"DEBIAN-CVE-2021-20235","description":"There's a flaw in the zeromq server in versions before 4.3.3 in src/decoder_allocators.hpp. The decoder static allocator could have its sized changed, but the buffer would remain the same as it is a static buffer. A remote, unauthenticated attacker who sends a crafted request to the zeromq server could trigger a buffer overflow WRITE of arbitrary data if CURVE/ZAP authentication is not enabled. The greatest impact of this flaw is to application availability, data integrity, and confidentiality.","status":"published","published":"2021-04-01T14:15:13.217Z","modified":"2026-10-23T18:04:48.840746131Z","cvss":[{"version":"3.1","score":8.1,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"high"}],"updated_at":"2026-11-02T15:45:34.311861Z"},{"id":"JLSEC-2026-515","description":"There's a flaw in the zeromq server in versions before 4.3.3 in `src/decoder_allocators.hpp`. The decoder static allocator could have its sized changed, but the buffer would remain the same as it is a static buffer. A remote, unauthenticated attacker who sends a crafted request to the zeromq server could trigger a buffer overflow WRITE of arbitrary data if CURVE/ZAP authentication is not enabled. The greatest impact of this flaw is to application availability, data integrity, and confidentiality.","status":"published","published":"2026-05-20T04:02:19.667Z","modified":"2026-07-25T18:24:33.51170839Z","cvss":[{"version":"2.0","score":6.8,"vector":"AV:N/AC:M/Au:N/C:P/I:P/A:P","level":"medium"},{"version":"3.1","score":8.1,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"high"}],"updated_at":"2026-11-02T15:47:18.573531Z"},{"id":"UBUNTU-CVE-2021-20235","description":"There's a flaw in the zeromq server in versions before 4.3.3 in src/decoder_allocators.hpp. The decoder static allocator could have its sized changed, but the buffer would remain the same as it is a static buffer. A remote, unauthenticated attacker who sends a crafted request to the zeromq server could trigger a buffer overflow WRITE of arbitrary data if CURVE/ZAP authentication is not enabled. The greatest impact of this flaw is to application availability, data integrity, and confidentiality.","status":"published","published":"2021-04-01T14:15:00Z","modified":"2026-04-22T12:45:40.984169Z","cvss":[{"version":"3.1","score":8.1,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","level":"high"}],"updated_at":"2026-11-02T15:54:25.728622Z"},{"id":"DLA-2588-1","title":"zeromq3 - security update","status":"published","published":"2021-03-09T00:00:00Z","modified":"2026-03-09T01:22:12.723324Z","updated_at":"2026-11-02T15:46:10.712745Z"},{"id":"USN-4920-1","title":"zeromq3 vulnerabilities","description":"It was discovered that ZeroMQ incorrectly handled certain application\nmetadata. A remote attacker could use this issue to cause ZeroMQ to crash,\nor possibly execute arbitrary code. (CVE-2019-13132)\n\nIt was discovered that ZeroMQ mishandled certain network traffic. An\nunauthenticated attacker could use this vulnerability to cause a denial-of-\nservice and prevent legitimate clients from communicating with ZeroMQ.\n(CVE-2020-15166)\n\nIt was discovered that ZeroMQ did not properly manage memory under certain\ncircumstances. If a user or automated system were tricked into connecting\nto one or multiple compromised servers, a remote attacker could use this\nissue to cause a denial of service. (CVE-2021-20234)\n\nIt was discovered that ZeroMQ incorrectly handled memory when processing\nmessages with arbitrarily large sizes under certain circumstances. A remote\nunauthenticated attacker could use this issue to cause a ZeroMQ server to crash,\nresulting in a denial of service, or possibly execute arbitrary code. This issue\nonly affected Ubuntu 18.04 ESM and Ubuntu 20.04 ESM. (CVE-2021-20235)\n\nIt was discovered that ZeroMQ did not properly manage memory under certain\ncircumstances. A remote unauthenticated attacker could use this issue to\ncause a ZeroMQ server to crash, resulting in a denial of service. This issue\nonly affected Ubuntu 18.04 ESM and Ubuntu 20.04 ESM. (CVE-2021-20237)\n","status":"published","published":"2022-06-15T18:16:23Z","modified":"2026-06-29T13:48:53.719481649Z","updated_at":"2026-11-02T16:58:15.159055Z"}]}}